The aim of this project is to examine the lipid clearing mechanism, the interaction between the enzymes and cofactors (apolipoproteins) regulating this process and the relationship between lipase(s) levels, exogenous (infused) lipid, heparin and endogenously synthesized triglycerides, (very low density lipoproteins VLDL) and cholesterol (lipoprotein-X). These studies will be carried out in premature, parenterally fed infants and in newborn animals, where not feasable in humans. Answers to the following questions will be sought: 1. What is the effect of lipid infusion on endothelial and tissue lipase levels (lipoprotein lipase-LPL, and hepatic lipase-HL)? 2. What is the effect of the type of lipid infused? 3. What is the effect of lipid infusion on the composition of aerum lipids? 4. What is the relationship between lipid infusion, the appearance of Lipoprotein-X (LP-X) and the activity of lecithin cholesterol acyl transferase (LCAT) in the circulation of very low birth weight (VLBW) infants? 5. What is the role of hepatic lipase in the process of lipid clearing in VLBW infants? These questions will be answered by studies of the endothelial and tissue lipases in newborn animals maintained on regimens similar to the ones employed in the management of parenterally fed preterm infants and by studies of the heparin releasable endothelial lipases: lipoprotein lipase (LPL) and hepatic lipase (HL), quantitated in serum as post heparin lipolytic activity - PHLA, in infants maintained on total parenteral nutrition in the intensive care nursery. Since VLBW infants are maintained exclusively on parenteral nutrition and receive lipid infusion for long periods, a better understanding of all aspects of the lipid clearing mechanism is necessary for the optimal management of these very premature infants. These studies are also leading to development of rapid and highly accurate non-invasive tests of the lipid clearing ability of preterm infants.